This invention relates to facsimile transmitters and/or transceivers of the type utilized to transmit information-bearing signals representing the dark/light variations on a document located at a transmitter or transceiver and converting the information-bearing signals to marks or images on a copy medium located at a receiver so as to form a copy which is a reasonable facsimile of the original document.
It is common in facsimile apparatus to set a predetermined voltage or current level which represents white on a document. Typically, this predetermined voltage or current level is set at the factory. However, as the light source of a scanner ages, the scanner phototransistor ages and the alignment between light source and phototransistor changes, the magnitude of the predetermined voltage or current level will vary and the preset light level will no longer be appropriate.
Heretofore, it has been suggested that the document should be preliminarily scanned so as to determine characteristics so as to appropriately set the white gain of the transmitter amplifier means. However, such preliminary scanning can be time consuming, and the consumption of time can be extremely undesirable in unattended facsimile transmitters wherein the time consumed between transmissions should be minimized. Moreover, the gain itself in prior art facsimile transmitters may be subject to some drift even over a relatively short period corresponding to the time required to scan a single document.
In general, it is desirable to achieve the maximum output from a facsimile transmitter which is allowed by the rules and regulations of the FCC for purposes of transmission over the telephone network. In a typical facsimile transmitter, the output from the transmitter when set at the factory may not be maximized for a given document. In other words, a given document may have a characteristic which will not permit the full output of the transmitter to be utilized.